Champ 5F1

[dpm309]

I am working on a Champ 5F1 clone that has a shorted PT.  I disconnected the power rail and removed the tubes and my light limiter is still showing a short.  The HV secondary windings are only reading 25VAC on one side and less than 1VAC on the other so I am sure it is fried.  The owner had a Hammond AC271X (560VAC @ 70ma) that he said came with the kit.  If I am not wrong, the 5F1 should have at least 650VAC.  I ordered a Weber PT that has both 600 and 660VAC on the secondary.  The amp worked before the PT blew.  My question is why would the Hammond PT be included in a 5F1 kit and should I use the 600V or the 660V taps?  All of the components match what a Champ should be except for the addition of a tone and master volume control.

Dan

[tubeswell]

Lots of people choose mix'n'match parts for their builds, even in kit form.  With 280-0-280@70mA and a 5V@2A rectifier winding, I'm guestimating they'd expect around 300V on the 6V6 plate if they use a 5Y3G, or around 360V if they use a 5AR4. A cathode biased SE 6V6 sounds good at around 350-360 with about 36-40mA of idle current. But if you want to use a 6L6, it will pull down the B+ more, and at  (say) about 300V on the plate, you'd probably need to run it at 70mA to get proper Class A operation - which is at the limit of that PT.

[dpm309]

The amp is using a 5Y3 rectifier tube and 6V6 power tube so the new PT should be able to get the plate voltage up to the 350-360 range.  I am going to experiment with both the 600 and 660 HV windings to see what voltages I get and how it sounds.  Might be a delay in getting the PT since some *SOB* hacked my Visa card I had to close it out and wait a week for a new card so I can reorder from Weber.

Dan

[PRR]

Hoffman has a for-Champ PT.

[dpm309]

Got the PT today and installed it and it sounds good with using either the 600 or 660V secondaries.  My voltages are as follows:

600V Secondaries:
12AX7  P2- 206, P3 and 8 - 1.1, P6 - 186
6V6      P3 - 364, P4 - 335, P8 - 19
B+ - 376, B+1 - 335, B+2 - 293

660V Secondaries:
12AX7  P2- 225, P3 and 8 - 1.2, P6 - 202
6V6      P3 - 396, P4 - 366, P8 - 21
B+ - 410, B+1 - 367, B+2 - 318

Which should I use?  As I don't hear any appreciable difference, I am leaning towards using the 600V to increase the tube life.  Any suggestions or comments?

Thanks,

Dan

[balcorn80]

Just a warning about Weber PTs: I've been using them a little bit for the past year and have opened the amps up less than 90 days later to find the leads(heaters, HV, and primaries) hard and cracked and the wire was exposed. I have seen this INSIDE THE BELLS FOR THE TRANSFORMERS which caused the hv taps to short out against the bells of the transformer, effectively roasting the PT. I would, if it were on my bench and I didn't have the option of using a different PT(which would be my first choice) take the bells off and put shrink tubing on the leads all the way up to the bobbin, especially where they may be bent/curved to go through the end bells, and I would also make sure that anywhere there is a curve in the wire outside the bells that there was shrink tubing there.

Just my suggestion/experience. When I called Weber, they seemed to know it was an issue and reccomended putting the shrink tubing on prior to any use.

[HotBluePlates]

It seems like your 600v wiring results in voltages closer to original stock. That's what I'd use.

[Fresh_Start]

Lots of people choose mix'n'match parts for their builds, even in kit form.  With 280-0-280@70mA and a 5V@2A rectifier winding, I'm guestimating they'd expect around 300V on the 6V6 plate if they use a 5Y3G, or around 360V if they use a 5AR4. A cathode biased SE 6V6 sounds good at around 350-360 with about 36-40mA of idle current. But if you want to use a 6L6, it will pull down the B+ more, and at  (say) about 300V on the plate, you'd probably need to run it at 70mA to get proper Class A operation - which is at the limit of that PT.

Personally, I'd try to find a PT with 275-0-275 secondaries.  With a real 5Y3 rectifier, that should put about 300 volts on the 6V6 plate and 260ish on the 12AX7 plates.  I played around a lot with voltages in a 5F2-A build and that's what sounded best to me - warm & early but gradual breakup.  That's about where the 5E1 voltages were.  However, if you want more clean headroom and volume, then your 300-0-300 secondaries get close to a Blackface Champ's voltages.  There's no "wrong" answer within reason.

BTW a Sovtek "5Y3" (which ain't) would raise B+ by 20-25 volts. 

Cheers,

Chip

[dpm309]

Thanks for all of the suggestions.  I ended up using the 300-0-300 secondaries.  Also, I have an NOS GE 5Y3GT that I tried and as Chip mentioned, did lower the B+ about 25 Volts as compared to the Sovtek 5Y3.  Don't know if I want to part with the GE but I will let the owner decide which sound better.  As far as problems with the Weber PT, they did state to look at all of the leads for cracks, etc and to shrink wrap any leads that look suspicious so they seem to be aware of the problem.

Dan

[Willabe]

As far as problems with the Weber PT, they did state to look at all of the leads for cracks, etc and to shrink wrap any leads that look suspicious so they seem to be aware of the problem.

That's just plain wrong on Webers part IMO. Sounds like they got a batch of PT's/OT's made with bad fly lead wire insulation. I don't want to see them go under but that's kind of a funky way to get out from under it?   


                       Brad